The invention relates, in general, to an apparatus for controlling an elevator based upon load, and, in particular, to an apparatus for determining whether to stop an elevator for a floor call based upon the current load in the elevator and the anticipated load to be added by stopping for the floor call.
Prior art automatic elevator controls typically include a selector for generating a signal representing the next floor along the path of travel of the elevator at which the elevator could stop. These controls also include a circuit for comparing the selector signal with floor calls stored in a memory. When a floor call and the selector signal match, the control signals the elevator to stop.
All elevators have weight limits imposed upon them to prevent them from becoming from overloaded. For example, some form of load sensing device is located in the elevator car to generate a signal corresponding to the load being carried by the elevator car. Typical devices measure either the actual weight or the number of passengers in the elevator car. Also, certain predetermined load limits can be imposed which may vary according to the traffic conditions. For example, the load limit may be adjusted to a low value during light traffic conditions and to a higher value during heavy traffic conditions, whereby the waiting times of the passengers at the floors can be reduced by having an elevator that has reached its load limit bypass the floor.
U.S. Pat. No. 3,504,770 discloses an elevator control for downward peak traffic. High load limit values are set corresponding to the traffic density expected Furthermore, each elevator is assigned to a certain number of floors, for example three, where at the lower one of the floors, all waiting passengers can be picked up and the elevator car will be approximately fully loaded. If the load value limit is reached at the floor above the lower floor, the elevator car will be caused to pass the lower floor. If the elevator stops but can not pick up all of the waiting passengers due to reaching the load limit value, a second elevator car must be utilized to serve the same floor, which causes increased time losses with respect to the entire elevator system.
U.S. Pat. Nos. 3,967,702; 3,973,649 and 4,030,572 all relate to a group elevator control which detects the number of passengers in the cars and the number of passengers waiting at the floors, and, based upon the hall calls and car calls registered, calculates the number of passengers traveling to various floors utilizing predetermined ratios. Hall call assignment is inhibited only after a load limit has been exceeded. Thus, an already overloaded car will continue to stop at hall calls which previously had been assigned to it.